The present invention relates to an information recording medium such as a DVD (Digital Versatile Disk)-RAM (Random Access Memory) which is used to record predetermined information. The present invention also relates to a cutting apparatus for recording header data on a master for the information recording medium by exposure. Furthermore, the present invention relates to an information reproducing apparatus for reproducing the information recorded on the information recording medium. More specifically, the present invention relates to an address mark indicating the recording position of address data included in header data.
A plurality of sector fields are formed on an optical disk as the above information recording medium. Each of these sector fields includes a header field and a recording field. Header data is recorded in the header field in advance by embossing. User data is recorded in the recording field by using phase change. A VFO (Voltage Frequency Oscillator) field, an AM (Address Mark) field, and a PID (Physical ID) field are sequentially arranged in the header field. A continuously repeated pattern is recorded in the VFO field. An address mark indicating the recording position of address data is recorded in the AM field by embossing. Various data including address data are recorded in the PID field by embossing.
Data are recorded on such an optical disk by using run length limited code sequences having their run lengths limited in a predetermined range except for specific fields (e.g., AM fields). A run length represents the number of consecutive, identical channel bits. No run length code sequence includes a run of is (in channel bits). A run length in this specification therefore represents a run of 0s (in channel bits). For example, data to be recorded according to a run length limitation corresponding to run lengths of 2 to 10 includes no consecutive 1s. In addition, the run length of 0s between 1s is limited to 2 to 10. Such a run length limitation corresponding to run lengths of 2 to 10 is abbreviated as RLL (2, 10). Note that RLL is an abbreviation for "Run Length Limited".
Data to be recorded in each recording field of the optical disk is encoded into fixed-length block codes. A fixed-length block code is a code which is generated by encoding data at a constant ratio of code words to data words, e.g., 2:1. In demodulating such a fixed-length block code, if a block boundary is mistaken, proper modulation cannot be performed. For this reason, an address mark is recorded in an AM field set before encoded data to allow detection of a proper block boundary in reproducing data, thereby demodulating the data. If a portion on which data is recorded is mistaken as an address mark, subsequent data cannot be normally demodulated.
Note that in the edge recording scheme, NRZI (Non Return to Zero Inverted) processing is performed to invert the polarity of data at a position corresponding to each channel bit "1".
If pits representing a repeated pattern recorded in the above VFO field includes a defective pit which cannot be recognized as a pit, the following problem is posed. When the header field having a VFO field including a defective pit is reproduced, the reproduced pattern obtained is affected by the defective pit. The reproduced pattern affected by the defective pit then causes a detection error of an address mark. If an address mark is erroneously detected, the proper address data cannot be obtained. As a result, the optical disk cannot be normally played.